I also have a Maxwell matte only screen and can confirm its brighter and more contrasty than the stock Mamiya. The Mamiya, however, is far from bad and can be rather close in performance in good light. Another advantage of the Maxwell is that its clearly easier to focus on spots nearer to the edges, but as you know focus accuracy is best in the center. Since the Maxwell screens are expensive, I think its worthwhile if you use the RZ a fair bit or in poorer light, less so if you use it occasionally.